Method of forming interconnection structure having notches for semiconductor device

ABSTRACT

A semiconductor device is disclosed. The device includes a substrate, a first dielectric layer disposed over the substrate and a metal structure disposed in the first dielectric layer and below a surface of the first dielectric layer. The metal structure has a such shape that having an upper portion with a first width and a lower portion with a second width. The second width is substantially larger than the first width. The semiconductor device also includes a sub-structure of a second dielectric positioned between the upper portion of the metal structure and the first dielectric layer.

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/778,799, filed on Mar. 13, 2013, the entire disclosure ofwhich is hereby incorporated herein by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth in the past several decades. Technological advances insemiconductor materials and design have produced increasingly smallerand more complex circuits. These material and design advances have beenmade possible as the technologies related to processing andmanufacturing have also undergone technical advances. As a size of thesmallest component has decreased, numerous challenges have risen. Forexample, interconnects of conductive lines and associated dielectricmaterials that facilitate wiring between the transistors and otherdevices play a more and more important role in IC performanceimprovement. It is desired that metallization for interconnectionstructures be robust, and improvements in this area are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with accompanying figures. It is emphasized that,in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposeonly. In fact, the dimension of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a flowchart of an example method for fabricating asemiconductor integrated circuit (IC) constructed according to variousaspects of the present disclosure.

FIGS. 2 to 9B are cross-sectional views of an example semiconductor ICdevice at fabrication stages constructed according to the method of FIG.1.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

FIG. 1 is a flowchart of one embodiment of a method 100 of fabricatingone or more semiconductor devices according to aspects of the presentdisclosure. The method 100 is discussed in detail below, with referenceto a semiconductor device 200 shown in FIGS. 2 to 9B for the sake ofexample.

Referring to FIGS. 1 and 2, the method 100 begins at step 102 byproviding a substrate 210. The substrate 210 includes silicon.Alternatively or additionally, the substrate 210 may include otherelementary semiconductor such as germanium. The substrate 210 may alsoinclude a compound semiconductor such as silicon carbide, galliumarsenic, indium arsenide, and indium phosphide. The substrate 210 mayinclude an alloy semiconductor such as silicon germanium, silicongermanium carbide, gallium arsenic phosphide, and gallium indiumphosphide. In one embodiment, the substrate 210 includes an epitaxiallayer. For example, the substrate 210 may have an epitaxial layeroverlying a bulk semiconductor. Furthermore, the substrate 210 mayinclude a semiconductor-on-insulator (SOI) structure. For example, thesubstrate 210 may include a buried oxide (BOX) layer formed by a processsuch as separation by implanted oxygen (SIMOX) or other suitabletechnique, such as wafer bonding and grinding.

The substrate 210 may also include various p-type doped regions and/orn-type doped regions, implemented by a process such as ion implantationand/or diffusion. Those doped regions include n-well, p-well, lightdoped region (LDD), heavily doped source and drain (S/D), and variouschannel doping profiles configured to form various integrated circuit(IC) devices, such as a complimentary metal-oxide-semiconductorfield-effect transistor (CMOSFET), imaging sensor, and/or light emittingdiode (LED). The substrate 210 may further include other functionalfeatures such as a resistor or a capacitor formed in and on thesubstrate.

The substrate 210 may also include various isolation features. Theisolation features separate various device regions in the substrate 210.The isolation features include different structures formed by usingdifferent processing technologies. For example, the isolation featuresmay include shallow trench isolation (STI) features. The formation of aSTI may include etching a trench in the substrate 210 and filling in thetrench with insulator materials such as silicon oxide, silicon nitride,or silicon oxynitride. The filled trench may have a multi-layerstructure such as a thermal oxide liner layer with silicon nitridefilling the trench. A chemical mechanical polishing (CMP) may beperformed to polish back excessive insulator materials and planarize thetop surface of the isolation features.

The substrate 210 may also include gate stacks formed by dielectriclayers and electrode layers. The dielectric layers may include aninterfacial layer (IL) and a high-k (HK) dielectric layer deposited bysuitable techniques, such as chemical vapor deposition (CVD), atomiclayer deposition (ALD), physical vapor deposition (PVD), thermaloxidation, combinations thereof, or other suitable techniques. Theelectrode layers may include a single layer or multi layers, such asmetal layer, liner layer, wetting layer, and adhesion layer, formed byALD, PVD, CVD, or other suitable process.

The substrate 210 may also include a plurality of inter-level dielectric(ILD) layers and conductive features integrated to form an interconnectstructure configured to couple the various p-type and n-type dopedregions and the other functional features (such as gate electrodes),resulting a functional integrated circuit. In one example, the substrate210 may include a portion of the interconnect structure and theinterconnect structure includes a multi-layer interconnect (MLI)structure and an ILD layer integrated with a MLI structure, providing anelectrical routing to couple various devices in the substrate 210 to theinput/output power and signals. The interconnect structure includesvarious metal lines, contacts and via features (or via plugs). The metallines provide horizontal electrical routing. The contacts providevertical connection between silicon substrate and metal lines while viafeatures provide vertical connection between metal lines in differentmetal layers.

The substrate 210 also includes conductive features, represented byconductive features 214 in FIG. 2. The conductive features 214 mayinclude doped regions (such as sources or drains), or gate electrodes.Alternatively, the conductive features 214 may include electrodes,capacitors, resistors or a portion of resistors. The conductive features214 may also include a portion of the interconnect structures, such ascontacts, metal vias, or metal lines. The conductive features 214 may beformed by a procedure including lithography, etch and deposition.

Referring to FIGS. 1 and 3, the method 100 proceeds to step 104 bydepositing a first dielectric layer 310 over the substrate 210 and afirst hard mask 330 over the first dielectric layer 310. The firstdielectric layer 310 includes dielectric materials, such as siliconoxide, silicon nitride, a dielectric material having a dielectricconstant (k) lower than thermal silicon oxide (therefore referred to aslow-k dielectric material layer), or other suitable dielectric materiallayer. In various examples, the low k dielectric material may includefluorinated silica glass (FSG), carbon doped silicon oxide, amorphousfluorinated carbon, Parylene, BCB (bis-benzocyclobutenes), polyimide,and/or other materials as examples. In another example, the low kdielectric material may include an extreme low k dielectric material(ELK). A process of forming the dielectric material layer 310 mayutilize spin-on coating or CVD.

The first hard mask 330 may include materials having a substantiallyslow etch rate compared to the first dielectric layer 310 in a lateretching process. For example, the first hard mask includes siliconnitride, silicon oxide, silicon oxynitride, or other suitable material.In one embodiment, a first capping layer is interposed between the firstdielectric layer 310 and the first hard mask 330. The first cappinglayer may include silicon carbide, silicon carbide nitride, siliconnitride, carbon doped oxide dielectrics comprised of Si, C, O, and H(SiCOH), or other suitable materials. The first hard mask layer 330, aswell as the first capping layer may be deposited by ALD, CVD or PVDprocess.

Referring to FIGS. 1 and 4, the method 100 proceeds to step 106 bypatterning the first hard mask 330. The first hard mask 330 may bepatterned by lithography and etch processes. For example, a patternedphotoresist may be formed on the first hard mask 330 by lithographyprocesses and an etch process may follow to etch the first hard mask 330through the patterned photoresist to form an opening 335 on the firsthard mask. The opening 335 may be aligned to the respective conductivefeatures 214 to define a vertical interconnection (to be formed).Alternatively or additionally, the opening 335 may also be aligned to anarea where the conductive features 214 are absent to define a horizontalinterconnection.

Referring to FIGS. 1 and 5, the method 100 proceeds to step 108 byforming a trench 410 in the first dielectric layer 310 and filling thetrench 410 with a first metal layer 414 to form a first metal structure416. The trench 410 is formed by etching the first dielectric layer 310through the patterned first hard mask 330. The etch process includes wetetch, dry etch, or a combination thereof. In the present embodiment, thetrench 410 is formed with a substantially straight sidewall profile.

In one embodiment, a first barrier layer 412 is filled in the trench 410first to prevent diffusion and/or provide material adhesion. The firstbarrier layer 412 may include titanium nitride (TiN), tantalum nitride(TaN), tungsten nitride (WN), titanium silicon nitride (TiSiN), tantalumsilicon nitride (TaSiN), or other suitable materials. The first metallayer 414 is then deposited on the first barrier layer 412. The firstmetal layer 414 may include aluminum (Al), copper (Cu) or tungsten (W)or other suitable conductive material. The first barrier layer 412 andthe first metal layer 414 may be deposited by ALD, PVD, CVD, or othersuitable process. With the substantially straight sidewall profile ofthe trench 410, a process window of metal layers filling in can be muchmore relaxed.

In the depicted embodiment, the metal layer 414 may exceed the firstmetal structure 416. Excess portions of the first metal layer 414, aswell as the first barrier layer 412, may be removed by a chemicalmechanical polishing (CMP) process. Additionally, the patterned firsthard mask 330 and the first capping layer 320 are removed during therecess.

Referring to FIGS. 1, 6A and 6B, the method 100 proceeds to step 110 bydepositing and then patterning a second hard mask 530 on the first metalstructure 416 and the first dielectric layer 310. In one embodiment, asecond capping layer is interposed between the first metal structure 416and the dielectric layer 310 and the second hard mask 530. The secondcapping layer may be similar in many respects to the first capping layerdiscussed above. The second hard mask 530 includes materials which havea substantially slow etch rate comparing to etch rates of the firstmetal structure 416 and the first dielectric layer 310 in a lateretching process. For example, the second hard mask 530 includes siliconcarbide, silicon carbide nitride, silicon nitride, carbon doped oxidedielectrics comprised of Si, C, O, and H (SiCOH), or other suitablematerials. The second hard mask 530 may be deposited by ALD, CVD, orother suitable processes. A procedure of patterning the second hard mask530 is similar in many respects to patterning the first hard mask 330discussed above in FIG. 4.

In the present embodiment, an opening 535 is formed in the patternedsecond hard mask 530, and is offset-aligned to one side of the firstmetal structure 416, as shown in the FIG. 6A. The opening 535 extendsfrom the portion of the first metal structure 416 to adjacent firstdielectric layer 310. Alternatively, two offset openings 535 are alignedto each side of the first metal structure 416, as shown in FIG. 6B. Forthe sake of reference, the two offset openings are assigned referencenumbers 535A and 535B. Openings 535A and 535B extend to respectiveadjacent first dielectric layer 310. In the present embodiment, theopening 535A is separated with the opening 535B.

Referring to FIGS. 1, 7A and 7B, the method 100 proceeds to step 112 byetching a portion of the first metal structure 416 and the firstdielectric layer 310 through the opening 535 to form a notch 610. Thenotch 610 defines the first metal structure 416 as a two-portionstructure, which has a lower portion having the first width w₁ and afirst height h₁, and an upper portion having a second width w₂ and asecond height h₂. The second width w₂ is substantially smaller than thefirst width w₁. Alternatively notches 610 are formed on each side of thefirst metal structure 416 through openings 535A and 535B, and they arereferred to as 610A and 610B.

The etching process may include wet etch, dry etch, or a combinationthereof. The dry etching process may implement fluorine-containing gas(e.g., CF4, SF6, CH2F2, CHF3, and/or C2F6), chlorine-containing gas(e.g., Cl2, CHCl3, CCl4, and/or BCl3), bromine-containing gas (e.g., HBrand/or CHBR3), iodine-containing gas, other suitable gases and/orplasmas, and/or combinations thereof. The etching process may include amultiple-step etching to gain etch selectivity, flexibility and desiredetch profile. In one embodiment, the notch 610 is formed with a verticalsidewall profile, as shown in FIGS. 7A and 7B. In another embodiment,the notch 610 is formed with a taper sidewall profile, having a widertop opening, as shown in FIGS. 7C and 7D.

In one embodiment, the portion of the first metal structure 416 and thefirst dielectric layer 310 are etched simultaneously and by adjusting anetch rate ratio of the first metal structure 416 to the first dielectriclayer 310, the notch 610 can be formed in various bottom profiles. Forexample, when the etch rate of the first metal structure 416 iscontrolled to be substantially larger than the etch rate of the firstdielectric layer 310, the notch 610 is formed a non-flat bottom profilehaving a deeper portion in a side of the first metal structure 416, asshown in FIG. 7E. For another example, when the etch rate of the firstmetal structure 416 is controlled to be substantially slower than theetch rate of the first dielectric layer 310, the bottom profile of thenotch 610 has a deeper portion at a side of the first dielectric layer310, as shown in FIG. 7F. The etch rate ratio may be controlled byadjusting etching process parameters, such as etchants used, pressure,power, RF bias voltage, etchant flow rate, and other suitableparameters.

Referring to FIGS. 1, 8A to 8B, the method 100 proceeds to step 114 byfilling in the notch 610 with a second dielectric layer 640 to form adielectric sub-structure 650. The second dielectric layer 640 includessilicon carbide, silicon carbide nitride, silicon nitride, SiCOH, orother suitable materials. In one embodiment, the second dielectric layer640 is formed with a material different from the first dielectric layer310. The second dielectric layer 640 may be deposited by ALD, CVD andother suitable processes. In one embodiment, a second barrier layer 645is deposited selectively on the first metal structure 416 in the notch610 first and the second dielectric layer 640 is deposited on the secondbarrier layer 645 and fills in the notch 610. The second barrier layer645 may prevent diffusion and/or improve adhesion between the firstmetal structure 416 and the second dielectric layer 640. The secondbarrier layer 645 includes metals, such as cobalt (Co), and may bedeposited by ALD or CVD. Additionally, a CMP process is applied toremove excessive the second dielectric layer 640.

With the dielectric sub-structure 650, the first metal structured 416 isconfigured with a lower portion and an upper portion. In the presentembodiment, the lower portion is referred to as a trench metal and theupper portion as avia metal of an interconnection. The second width w₂is a critical dimension (CD) of the via metal. In one embodiment, aratio of h₂ to h₁ is in a range from 0.25 to 4.0. Since both trenchmetal and via metal are formed by one metal layer, the first metal layer414, the via metal is formed with a pseudo-self-alignment nature to thetrench metal. In one embodiment, with the tapered notch 610, the viametal is formed with a taper sidewall profile having a smaller dimensionat its top portion comparing to its bottom portion. In anotherembodiment, with a flat bottom profile of the notch 610, the trenchmetal has a flat bottom profile. In yet another embodiment, with anon-flat bottom profile of the notch 610, the trench metal has anon-flat bottom profile.

Additional steps can be provided before, during, and after the method100, and some of the steps described can be repeated, replaced,eliminated, or moved around for additional embodiments of the method100. As an example, the steps 104 to 108 are repeated to form a newmetal/dielectric interconnection 700 over the first metal structure 416.The new metal/dielectric interconnection 700 may include a thirddielectric layer 710, a third barrier layer 712 and a second metal layer714, as shown in FIGS. 9A and 9B. The second metal layer 714, as well asthe third barrier layer 712, may align and contact to a respective viametal of the first metal structure 416 to form a verticalinterconnection.

Based on the above, the present disclosure offers a semiconductor devicewith a metal structure notched by a dielectric sub-structure. An upperportion of the metal structure serves as a via metal and a lower portionof the metal structure serves as a trench metal. The disclosure offersmethods for forming the via metal and the trench metal. The methodemploys forming a dielectric sub-structure by etching portions of themetal structure and portions of a dielectric layer. The method providesforming the via metal with a self-alignment nature to align to thetrench metal. The method has demonstrated a robust metal line formationfor interconnection structures.

The present disclosure provides many different embodiments of asemiconductor device. The semiconductor device includes a substrate, afirst dielectric layer disposed over the substrate and a metal structuredisposed in the first dielectric layer and below a surface of the firstdielectric layer. The metal structure has a such shape that having anupper portion with a first width and a lower portion with a secondwidth. The second width is substantially larger than the first width.The semiconductor device also includes a sub-structure of a seconddielectric positioned between the upper portion of the metal structureand the first dielectric layer.

In another embodiment, the present disclosure offers a method forfabricating a semiconductor device that provides one or moreimprovements over other existing approaches. In one embodiment, a methodfor fabricating a semiconductor device includes providing a substrate,forming a first dielectric layer over the substrate, forming a firsttrench in the first dielectric layer, filling in the first trench with afirst metal layer to form a metal structure with a first width, forminga notch in the metal structure and the first dielectric layer, whereinthe notch defines an upper portion with a second width and a lowerportion with the first width of the metal structure and filling in thenotch with a second dielectric layer.

In yet another embodiment, a method for fabricating a semiconductordevice includes providing a substrate, depositing a first dielectriclayer over the substrate, forming a patterned first hard mask over thefirst dielectric layer, etching the first dielectric layer through thepatterned first hard mask to form a first trench, filling in the firsttrench with a first metal layer to form a metal structure, forming apatterned second hard mask over the metal structure and the firstdielectric layer and removing a portion of the metal structure and aportion of the first dielectric layer to form a notch. The notch definesan upper portion and lower portion of the metal structure. A width ofthe upper portion is smaller than a width of the lower portion. Themethod also includes filling in the notch with a second dielectriclayer, depositing a third dielectric layer over the metal structure,forming a second trench in the third dielectric layer to expose at leasta portion of the upper portion of the metal structure and filling in thesecond trench with a second metal layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for fabricating a semiconductor device,the method comprising: depositing a first dielectric layer over asubstrate; forming a first trench in the first dielectric layer; fillingin the first trench with a first metal layer to form a metal structurewith a first width; forming a notch in the metal structure and the firstdielectric layer, wherein the notch defines an upper portion with asecond width and a lower portion with the first width of the metalstructure; filling in the notch with a second dielectric layer; andafter filling in the notch with the second dielectric layer, forming aconductive feature over the metal structure and the second dielectriclayer in the notch such that the conductive feature physically contactsthe metal structure and the second dielectric layer in the notch.
 2. Themethod of claim 1, wherein the second width of the upper portion of themetal structure is smaller than the first width of the lower portion ofthe metal structure.
 3. The method of claim 1, wherein the notch isformed by etching the metal structure and the first dielectric layerthrough a patterned first hard mask simultaneously.
 4. The method ofclaim 1, further comprising: filling in the first trench with a firstbarrier layer prior to filling in the first metal layer; and selectivelydepositing a second barrier layer on the metal structure in the notch,prior to filling in the second dielectric layer.
 5. The method of claim4, wherein the second barrier layer includes cobalt (Co).
 6. The methodof claim 1, further comprising: depositing a third dielectric layer overthe metal structure; and forming a second trench in the third dielectriclayer to expose at least a portion of the upper portion of the metalstructure, and wherein forming the conductive feature over the metalstructure and the second dielectric layer in the notch includes fillingin the second trench with a second metal layer.
 7. A method of forming astructure of a semiconductor device, the method comprising: depositing afirst dielectric layer over a substrate; forming a patterned first hardmask over the first dielectric layer; etching the first dielectric layerthrough the patterned first hard mask to form a first trench; filling inthe first trench with a first metal layer to form a metal structure;forming a patterned second hard mask over the metal structure and thefirst dielectric layer; removing a portion of the metal structure and aportion of the first dielectric layer to form a notch, wherein the notchdefines an upper portion and lower portion of the metal structure,further wherein a width of the upper portion is smaller than a width ofthe lower portion; filling in the notch with a second dielectric layer;depositing a third dielectric layer over the metal structure; forming asecond trench in the third dielectric layer to expose at least a portionof the upper portion of the metal structure; and filling in the secondtrench with a second metal layer, wherein the second metal layer coversthe second dielectric layer.
 8. The method of claim 3, furthercomprising: filling in the first trench with a first barrier layer priorto filling in the first metal layer; selectively depositing a secondbarrier layer on the metal structure in the notch, prior to filling inthe second dielectric layer; and filling in the second trench with athird barrier layer prior to filling in the second metal layer.
 9. Themethod of claim 8, wherein the second barrier layer includes cobalt(Co).
 10. A method of forming a structure of a semiconductor device, themethod comprising: depositing a first dielectric layer over a substrate;forming a metal structure in the first dielectric layer and below asurface of the first dielectric layer, the metal structure having ashape that includes: an upper portion with a first width; and a lowerportion with a second width, which is substantially larger than thefirst width, whereby a notch is formed in the metal structure; anddepositing a second dielectric sub-structure in the notch between theupper portion of the metal structure and the first dielectric layer; andafter depositing a second dielectric sub-structure in the notch, forminga conductive feature over the metal structure and the second dielectricsub-structure in the notch such that the conductive feature physicallycontacts the metal structure and the second dielectric sub-structure inthe notch.
 11. The method of claim 10, wherein the second dielectricsub-structure includes a flat bottom profile.
 12. The method of claim10, wherein the second dielectric sub-structure includes a non-flatbottom profile.
 13. The method of claim 12, wherein the seconddielectric sub-structure has a deeper portion adjacent a side of themetal structure.
 14. The method of claim 12, wherein the seconddielectric sub-structure has a deeper portion on a side of the firstdielectric layer.
 15. The method of claim 10, wherein the metalstructure has a relatively straight sidewall, except where notched bythe second dielectric sub-structure.
 16. The method of claim 15, whereinthe metal structure is notched on one side by the second dielectricsub-structure.
 17. The method of claim 15, wherein the metal structureis notched on two sides by the second dielectric sub-structures.
 18. Themethod of claim 10, wherein the upper portion of the first metalstructure has a taper sidewall profile, with a top width which issmaller than a bottom width.
 19. The method of claim 10, furthercomprising: a first barrier layer disposed between the metal structureand the first dielectric layer; and a second barrier layer disposedbetween the metal structure and the second dielectric sub-structure. 20.The method of claim 19, wherein the second barrier layer includes cobalt(Co) deposited selectively on the metal structure.